Aircraft, such as helicopters or vertically-landing airplanes, are often forced to choose a landing zone on unprepared ground. Rotor downdraft, poor weather, darkness, and other factors can make obstacles that have a relatively small radar cross-section, such as posts, wires, debris, and minor topological features, difficult to discern, either visually or via radar. This is sometimes referred to as a degraded visual environment (DVE). A DVE can result in hard or catastrophic landings, resulting in death, injury and/or equipment damage.
Numerous solutions have been proposed to aid pilots in such circumstances, but few have proven successful. In general, the radar returns of typical landing zone hazards are too low to be detected with a radar power return, rendering dangerous obstacles invisible to a pilot.